Higher order diffusion Monte Carlo propagators for linear rotors as diffusion on a sphere: Development and application to O_{2}@He_{n}
Abstract
Exploiting the theoretical treatment of particles diffusing on corrugated surfaces and the isomorphism between the "particle on a sphere" and a linear molecule rotation, a new diffusion kernel is introduced to increase the order of diffusion Monte Carlo (DMC) simulations involving linear rotors. Tests carried out on model systems indicate the superior performances of the new rotational diffusion kernel with respect to the simpler alternatives previously employed. In particular, it is evidenced a second order convergence toward exact results with respect to the time step of dynamical correlation functions, a fact that guarantees an identical order for the diffusion part of the DMC projector. The algorithmic advantages afforded by the latter are discussed, especially with respect to the "a posteriori" and "on the fly" extrapolation schemes. As a first application to the new algorithm, the structure and energetics of O_{2}@He_{n} (n = 140) clusters have been studied. This was done to investigate the possible cause of the quenching of the reaction between O_{2} and Mg witnessed upon increasing the size of superfluid He droplets used as a solvent. With the simulations on O_{2} indicating a strong localization in the cluster core, the behaviour as a function of n is ascribed to the extremely fluxional comportment of Mg@He_{n}, which dwells far from the droplet center, albeit being solvated, when n is large.
 Publication:

Journal of Chemical Physics
 Pub Date:
 September 2011
 DOI:
 10.1063/1.3639190
 Bibcode:
 2011JChPh.135k4504M
 Keywords:

 drops;
 isomorphism;
 liquid helium;
 Monte Carlo methods;
 oxygen;
 quenching (thermal);
 superfluidity;
 surface diffusion;
 68.35.Fx;
 81.40.Gh;
 66.10.x;
 Diffusion;
 interface formation;
 Other heat and thermomechanical treatments;
 Diffusion and ionic conduction in liquids